"The NHTSA is opening this investigation to evaluate the scope, frequency, and consequence of the alleged defect," the agency said in a statement.

The investigation is only a preliminary step, said Alan Adler, a G.M. spokesman. No crashes or injuries have been reported as a result of the issue, though one driver reported running over road debris while attempting to pull off the road.

The issue does not appear to affect the cars’ high-beam or fog lights, the NHTSA said. The owner complaints report that the issue is intermittent and the lights resume working after a period of time, particularly if the car is parked.